Mailgen: HTML injection vulnerability in plaintext e-mails

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS

• CVE-2025-59526: 0.44% estimated exploitation activity in the next 30 days; percentile 38.16 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

HTML Injection and XSS Filter Bypass in Plaintext Emails Summary An HTML injection vulnerability in plaintext emails generated by Mailgen has been discovered. Your project is affected if you use the Mailgen.generatePlaintext(email); method and pass in user-generated content. The issue was discovered and reported by Edoardo Ottavianelli (@edoardottt). Vulnerability Analysis The following function (inside index.js) is intended to strip all HTML content to produce a plaintext string. The process fails because it first converts HTML break tags to newlines and then attempts to strip HTML tags with a regular expression. Using a break tag inside another HTML tag can deceive the filter, allowing HTML content to be injected into the email. A valid payload is: <img<br src=xyz onerror=alert(1). Proof of Concept Resulting output file (emailText.txt): Mitigation The vulnerability has been patched in commit 741a019 and released to npm in version 2.0.30. Thanks to Edoardo Ottavianelli (@edoardottt)…

Published by the source

22 Sep 2025, 18:03 UTC

Last modified by the source

23 Sep 2025, 20:50 UTC

Source last checked

26 Oct 2026, 12:38 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-j2xj-h7w5-r7vp

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-j2xj-h7w5-r7vp

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# Patch Next advisory brief: CVE-2025-59526

Advisory: Mailgen: HTML injection vulnerability in plaintext e-mails
IDs: CVE-2025-59526, GHSA-j2xj-h7w5-r7vp
Record: https://patchnext.com/advisories/cve-2025-59526 (revision 2, source checked 26 Oct 2026, 12:38 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: mailgen 2.0.30. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm mailgen: affected < 2.0.30; fixed in 2.0.30

## Suggested inspection (read-only)
- `npm ls mailgen --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on mailgen.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-j2xj-h7w5-r7vp (OSV record GHSA-j2xj-h7w5-r7vp lists affected ranges: npm mailgen >=0 <2.0.30 (fixed))
- Verified: https://github.com/advisories/GHSA-j2xj-h7w5-r7vp (GitHub-reviewed advisory GHSA-j2xj-h7w5-r7vp lists affected ranges: npm mailgen >=0 <2.0.30)

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